drm/client: Add drm_client_modeset_check()

Add a way for client to check the configuration before comitting.

v2:
- Fix docs (Sam)
Reviewed-by: Sam Ravnborg <sam@ravnborg.org>
Signed-off-by: Noralf Trønnes <noralf@tronnes.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20200509141619.32970-5-noralf@tronnes.org

drivers/gpu/drm/drm_client_modeset.c

@@ -969,7 +969,7 @@ bool drm_client_rotation(struct drm_mode_set *modeset, unsigned int *rotation)
 }
 EXPORT_SYMBOL(drm_client_rotation);
 
-static int drm_client_modeset_commit_atomic(struct drm_client_dev *client, bool active)
+static int drm_client_modeset_commit_atomic(struct drm_client_dev *client, bool active, bool check)
 {
 	struct drm_device *dev = client->dev;
 	struct drm_plane *plane;
@@ -1036,7 +1036,10 @@ static int drm_client_modeset_commit_atomic(struct drm_client_dev *client, bool
 		}
 	}
 
-	ret = drm_atomic_commit(state);
+	if (check)
+		ret = drm_atomic_check_only(state);
+	else
+		ret = drm_atomic_commit(state);
 
 out_state:
 	if (ret == -EDEADLK)
@@ -1097,6 +1100,30 @@ static int drm_client_modeset_commit_legacy(struct drm_client_dev *client)
 	return ret;
 }
 
+/**
+ * drm_client_modeset_check() - Check modeset configuration
+ * @client: DRM client
+ *
+ * Check modeset configuration.
+ *
+ * Returns:
+ * Zero on success or negative error code on failure.
+ */
+int drm_client_modeset_check(struct drm_client_dev *client)
+{
+	int ret;
+
+	if (!drm_drv_uses_atomic_modeset(client->dev))
+		return 0;
+
+	mutex_lock(&client->modeset_mutex);
+	ret = drm_client_modeset_commit_atomic(client, true, true);
+	mutex_unlock(&client->modeset_mutex);
+
+	return ret;
+}
+EXPORT_SYMBOL(drm_client_modeset_check);
+
 /**
  * drm_client_modeset_commit_locked() - Force commit CRTC configuration
  * @client: DRM client
@@ -1115,7 +1142,7 @@ int drm_client_modeset_commit_locked(struct drm_client_dev *client)
 
 	mutex_lock(&client->modeset_mutex);
 	if (drm_drv_uses_atomic_modeset(dev))
-		ret = drm_client_modeset_commit_atomic(client, true);
+		ret = drm_client_modeset_commit_atomic(client, true, false);
 	else
 		ret = drm_client_modeset_commit_legacy(client);
 	mutex_unlock(&client->modeset_mutex);
@@ -1191,7 +1218,7 @@ int drm_client_modeset_dpms(struct drm_client_dev *client, int mode)
 
 	mutex_lock(&client->modeset_mutex);
 	if (drm_drv_uses_atomic_modeset(dev))
-		ret = drm_client_modeset_commit_atomic(client, mode == DRM_MODE_DPMS_ON);
+		ret = drm_client_modeset_commit_atomic(client, mode == DRM_MODE_DPMS_ON, false);
 	else
 		drm_client_modeset_dpms_legacy(client, mode);
 	mutex_unlock(&client->modeset_mutex);

include/drm/drm_client.h

@@ -162,6 +162,7 @@ int drm_client_modeset_create(struct drm_client_dev *client);
 void drm_client_modeset_free(struct drm_client_dev *client);
 int drm_client_modeset_probe(struct drm_client_dev *client, unsigned int width, unsigned int height);
 bool drm_client_rotation(struct drm_mode_set *modeset, unsigned int *rotation);
+int drm_client_modeset_check(struct drm_client_dev *client);
 int drm_client_modeset_commit_locked(struct drm_client_dev *client);
 int drm_client_modeset_commit(struct drm_client_dev *client);
 int drm_client_modeset_dpms(struct drm_client_dev *client, int mode);